San Francisco 49ers quarterback Troy Smith prepares to pass the ball during a football training session at their base in Watford, north London, Thursday, Oct. 28, 2010. The 49ers play the Denver Broncos in an NFL football match at Wembley Stadium on Sunday Oct. 31

Offensive coordinator Mike Johnson was a Ravens receivers coach during Troy Smith's rookie season in Baltimore, but don't think Johnson pulled any strings to get Smith the 49ers' starting quarterback job this week.

"I don't know if I had much decision," Johnson said, "but we talked about it."

Head coach Mike Singletary made the decision to start his third-stringer with Alex Smith sidelined by a separated left shoulder. Johnson's job is to make it work with someone who's been here only seven weeks.

Anyone who thinks the Johnson-Troy Smith connection of 2007 is relevant Sunday against the Broncos, that's the incorrect-answer buzzer you just heard.

"I knew Troy and I saw him practice and play the preseason games, but I didn't have a chance to coach him there," Johnson said. "I'm still basically learning what he does well."

Until this week, Johnson had barely seen Smith play since he signed with the 49ers on Sept. 6 - a personnel decision that came with no input from Johnson. Smith had only taken scout team snaps, and Johnson was meeting with Alex Smith during those drills.

Johnson knows Troy Smith is more mobile than the team's other quarterbacks, but he insists they won't change the playbook to suit his legs. Rather, Johnson said he has to "scale back" the game plan while still putting him to use.

"He has to go in there and play," Johnson said. "We're not going to hide him."

Jolly time: The 49ers' offensive line and Troy Smith got in a quick scrum with the Northampton Saints rugby club after practice, but it was just a friendly crash course in the other tackling sport.

No one got more air on "the line" than left tackle Joe Staley, who boasts of an unverified 40-inch vertical.

"I don't know much about rugby," Staley said after the quick rugby lesson and jersey exchange. "I've tried to watch it on TV, and I have no idea what's going on."

Briefly: Outside linebacker Ahmad Brooks (knee) returned to practice Thursday after missing a day. ... The 49ers signed safety Chris Maragos to the practice squad one day after cutting him from the 53-man roster.